262 A]snsruAL report Smithsonian institution, 1942 



to the mantle of mystery which surromided them and to intensify the 

 challenge which they presented. 



In 1935 a tangible characteristic material possessing virus activity 

 was isolated from Turkish tobacco plants diseased with tobacco mosaic 

 virus and made available for chemical study. The material, which 

 appeared to be a nucleoprotein of enormous size possessing quite dis- 

 tinctive properties, was obtained from every lot of diseased Turkish 

 tobacco plants examined. The same material was obtained from vari- 

 ous, in some instances unrelated, species, of mosaic-diseased plants. 

 Slightly different, although closely related, nucleoproteins were iso- 

 lated from plants diseased with strains of tobacco mosaic virus. The 

 purified preparations possessed properties which were characteristic, 

 not of the hosts in which they were produced, but of the virus or virus 

 strain. An unexpected finding was that mosaic-diseased Turkish 

 tobacco plants may contain as much as 1 part per 500 of the high 

 molecular weight nucleoprotein. The amount of material isolable 

 varied in other cases and appeared to depend upon the host and the 

 strain of the virus, and in some instances was only a small fraction 

 of the amount obtainable from mosaic-diseased Turkish tobacco 

 plants. To date all attempts to separate tobacco mosaic virus activity 

 from the nucleoprotein have failed and the material, which can be 

 obtained in the form of long thin paracrystalline needles (pi. 1, fig. 1) , 

 has come to be regarded as crystalline tobacco mosaic virus. The 

 material provided the first information regarding the general nature 

 and chemical makeup of this virus and, although its exact nature was 

 and remains a debatable matter, its isolation removed some of the 

 mystery surrounding the general nature of viruses and served as an 

 incentive for the search for similar materials in the case of other virus 

 diseases. 



The isolation of crystalline tobacco mosaic virus was followed by 

 the preparation from various virus-diseased tissues of over 20 crys- 

 talline or amorphous materials possessing some of the properties of 

 the respective viruses or virus strains. In not every case has it been 

 proved that the material is essentially pure and consists of virus. 

 However, in several cases it has been proved beyond a reasonable 

 doubt that the materials consist of the respective viruses in an essen- 

 tially pure state, and in no instance has virus activity been obtained 

 in the absence of the characteristic material. Owing chiefly to our 

 older ideas of the nature of viruses, the crystallinity of some of the 

 purified preparations may appear at first as a rather spectacular 

 property ; yet, if these materials are considered as proteins, crystallin- 

 ity becomes an expected rather than an unexpected property, for 

 many proteins are known to be crystallizable. Careful and mature 

 consideration will reveal that crystallinity or the lack of crystallinity 

 is of no special importance in connection with the purity or general 



